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Generation of the two-phase mesostructure of concrete: (a) aggregates, (b) cement matrix, (c) concrete merged by aggregates and cement matrix.
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In order to investigate the fracture behavior of concrete mesostructure and reveal the inner failure mechanisms which are hard to obtain from experiments, we develop a 3D numerical model based on the Voronoi tessellation and cohesive elements. Specifically, the Voronoi tessellation is used to generate the aggregates, and the cohesive elements are a...
Contexts in source publication
Context 1
... the generation of aggregates in concrete, a two-phase mesostructure of concrete can be generated easily by merging the cement matrix and aggregates as shown in Figure 3. Moreover, ITZ is an important component of the concrete mesostructure, it should be also considered in the model. ...
Context 2
... average stress-strain curve in the HF condition is shown in Figure 13. The numerical result is similar to the experimental one [46] in terms of peak stress and the curve shape. ...
Context 3
... strength of concrete is much higher than the one in the LF condition. To analyze the fracture patterns of concrete during the loading process, four typical states are chosen and marked in the stress-strain curve ( Figure 13). The fracture pattern (deformation is magnified 5 times) and the fracture surfaces of concrete in four different states are shown in Figure 14. ...
Context 4
... to the restraint effect of the loading surfaces, the cracks mainly occur at the middle part along the height direction, and the loading surfaces always remain complete during the loading process. The evolution of concrete fracture pattern (deformation is magnified 5 times) with the specimen height = 50 mm is shown in Figure 23. Due to the small specimen height, the fracture region of the concrete specimen is strongly affected by the restraint of the loading surfaces. ...
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Citations
... Figure 6 displays the failure modes of the compressive specimens. It is noticeable that the failure model closely resembles the semi-failure mode [28], [29]. Cracks initially appear at the middle heights of the specimens and parallel to the load direction. ...
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... Crack initiation and propagation is then computed by means of FEMs. The approach is extended in [19] where Voronoi cells are used to model the aggregates inside concrete. ...
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... Therefore, this model is rather limited. Voronoi diagrams have been used previously for simulating crack propagation via finite element methods [13,16]. In this work, we propose a novel method to synthesize crack structures in 3d images using Voronoi diagrams generated from random point processes. ...
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... In recent years, different damage models have been utilised to simulate the fracture process in concrete and fibre reinforced cementitious composites. Among them, concrete damage plasticity (CDP) method [17,[28][29][30][31], cohesive zone model (CZM) [32][33][34][35][36][37][38] and other discrete methods like the lattice-particle model [39,40] have been commonly used. CDP model considers the degradation of the elastic stiffness induced by plastic straining both in tension and compression based on the assumption of scalar (isotropic) damage. ...
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... There was no debonding of the print ers under the loading direction perpendicular to the interfaces, which agrees with ous studies [53][54][55]. To clarify the contribution of weak interlayer bond properties decrease in compressive strength, however, more comprehensive experimental t well as numerical modeling, are required [56][57][58]. Consequently, the negative e HPMC usage could be fully compensated by neither prolonged curing time nor fi inforcement. This is not only due to the weak interlayer areas in the specimens b the reduction of compressive strength on a mixture basis in the presence of HPMC ( 11). ...
... There was no debonding of the printed layers under the loading direction perpendicular to the interfaces, which agrees with previous studies [53][54][55]. To clarify the contribution of weak interlayer bond properties to the decrease in compressive strength, however, more comprehensive experimental tests, as well as numerical modeling, are required [56][57][58]. Consequently, the negative effect of HPMC usage could be fully compensated by neither prolonged curing time nor fiber reinforcement. This is not only due to the weak interlayer areas in the specimens but also the reduction of compressive strength on a mixture basis in the presence of HPMC (Figure 11). ...
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... First, due to lack of accurate experimental data, the shear fracture properties were assumed to be as same as those in normal direction. Also, the shear stress and normal stress are not fully coupled, which would be more important in compression mode [58]. Consequently, the model is not able to accurately simulate cracking induced by shear failure. ...
This paper presents a computational framework for modelling the fracture process in concrete under static and dynamic tensile loading considering its mesostructural characteristics. 3D mesostructure of concrete composed of real-shape coarse aggregates, mortar, interfacial transition zone between them and voids was developed using an in-house code based on Voronoi tessellation and splining techniques. Cohesive zone model was then employed to simulate the tensile fracture behaviour of concrete in terms of stress- and energy dissipation-displacement responses and crack mechanisms against the shape (spherical and irregular) and volume fraction (30%, 35% and 40%) of aggregate and strain rate (0, 1, 10 and 50 s-1). Results indicate that the irregular shape of aggregate has an important role in the micro-crack nucleation and ultimate fracture pattern but exhibits an insignificant effect on the tensile strength of concrete, which is mainly dependent on the strain rate and the random location and size distribution of aggregate.
... Besides the method mentioned above, a modified finite element method with cohesive elements is beginning to be used by more and more researchers [36][37][38][39][40][41][42][43][44]. The cohesive element is an interface transition element between solid elements. ...
... Based on our previous research works about the numerical model with cohesive element [43,44], in this paper, we adopt the Voronoi tessellation and zero thickness cohesive element to generate concrete mesostructure, and a modified constitutive model considering the inner friction effect is also adopted. On the basis of this numerical method, we investigate the fracture behavior of concrete under biaxial compression in terms of the mechanical behavior, fracture pattern, and energy evolution. ...
... The Voronoi tessellation can generate seamlessly connected polyhedron cells based on the predefined seeds, and normally one seed can only generates one polyhedron, which provides a certainty for aggregate generation. In this paper, we adopt the aggregate-generating method which has been presented in our previous work [44]. The typical Voronoi polyhedrons and the generated aggregates are shown in Figure 1. ...
The mechanical behavior of concrete under biaxial loading condition (especially biaxial compression) is one of the most important indexes to evaluate the quality of concrete. To study the mechanical behavior of concrete under biaxial compression at mesoscale, we adopted our recently developed 3D numerical model based on Voronoi tessellation and cohesive elements. A constitutive model considering the friction effect is used in the model to characterize the fracture behavior of all potential fracture surfaces inside the concrete. A series of numerical experiments with different biaxial compression stress ratios were carried out. It was found that with the increase of the biaxial compression ratio, the proportion of energy increment caused by friction stress increases. The effect of inner friction coefficient on the biaxial relative strength was also investigated, and this kind of study is hard to be carried out through laboratory experiments. The results show that the inner friction coefficient has a great influence on the biaxial relative strength of concrete, and there is a positive correlation between these two parameters. Based on the above rules, a conservative biaxial relative compression strength envelope is obtained by setting the inner friction coefficient as zero.
... However, because of the complex structure of porous media and the limitations of considering real geological conditions, conventional experiments and theoretical achievements fail in describing the uncertainties of flow and transport properties in porous media. For example, the continuous equivalent model averages the permeability of reservoirs and overlooks the influence stemming from the discontinuity caused by fractures [11,12]. This model is similar to the "black box" and its central problem is to solve the permeability tensor. ...
Coal contains a large number of fractures, whose characteristics are difficult to describe in detail, while their spatial distribution patterns may follow some macroscopic statistical laws. In this paper, several fracture geometric parameters (FGPs) were used to describe a fracture, and the coal seam was represented by a two-dimensional stochastic fracture network (SFN) which was generated and processed through a series of methods in MATLAB. Then, the processed SFN image was able to be imported into COMSOL Multiphysics and converted to a computational domain through the image function. In this way, the influences of different FGPs and their distribution patterns on the permeability of the coal seam were studied, and a finite element model to investigate gas flow properties in the coal seam was carried out. The results show that the permeability of the coal seam increased with the rising of fracture density, length, aperture, and with the decrease of the angle between the fracture orientation and the gas pressure gradient. It has also been found that large-sized fractures have a more significant contribution to coal reservoir permeability. Additionally, a numerical simulation of CBM extraction was carried out to show the potential of the proposed approach in the application of tackling practical engineering problems. According to the results, not only the connectivity of fractures but also variations of gas pressure and velocity can be displayed explicitly, which is consistent well with the actual situation.
